James l



1956 c. B. KNUDSON ETAL 2,772,320

ENGINE IGNITION SYSTEMS OR THE LIKE Filed Sept. 4, 1953 w. 5 F 2 L 0 /woE JAMES L. BUIE h w A CLARENCE B. muosou INVENTORS S7AET EON W I) g By MFREQUENCY" 'QP T THEIR ATTORNEY United States Patent ENGINE IGNITIONSYSTEMS OR THE LIKE Clarence B. Knudsen, Los Angeles, and James L. Buie, Sun Valley, Califl, assignors to Hoffman Electronics Corporation, acorporation of California Application September 4, 1953, Serial No.378,614

6 Claims. (Cl. 123-448) This invention pertains to improvements inignition systems such as are used with internal combustion engines. Morespecifically, the invention has to do with improvements applicable tothe ignition systems of relatively small and lightweight enginegenerators utilized as power supplies for portable or field use, such asin signalling or communication work. However, the principles of theinvention may also be utilized in larger equipments where desired.

The problem of producing a highly etficient yet highly compact portablepower supply has received considerable attention, especially as a resultof the ever-increasing communication needs of both military andcommercial organizations. The principal source of power for thesepurposes has been the electric battery, either of primary or secondarytype, although manually powered generators have found some limited use,as in emergency radios for life rafts and the like. Batteries, however,are rela tively bulky for any appreciable power drains, and have limitedshelf-life which does not recommend them for use in remote areas or inemergency or stand-by service. For these reasons, considerable efforthas been made to develop reliable and compact generators powered byinternal combustion engines. These have been fairly successful in unitsof moderate and large capacity, such as of the order of 1000 watts ormore, but really portable units (of the order of 100 to 1000 watts) havenot been forthcoming.

One of the difficulties inherent in previous approaches has been in thenecessity for providing for electrical ignition of the fuel mixture in avery small engine generator. Such a unit must be manually cranked .(toavoid the need for a starting battery), and its ignition, even whenstarting, must also be independent of a battery supply. On the otherhand, manual cranking means slow starting speeds, and low energy outputfrom a magneto or from the main generator. A magneto, if used,represents wasted space and weight since it performs no useful service(except during the starting phase) which cannot equally well be suppliedby the main generator after running speed has been attained.

A particularly compact form of small-capacity engine generator employsan alternating-current generator of the rotating permanent magnet type,direct-connected to a small gasoline engine. The voltage output of sucha unit will most conveniently be of the order of 120 volts or so, fordirect use (as in lighting) or for conversion or rectification forpowering telephone and radio equipment and the like. The output voltageof such a unit is very low at cranking speeds, and if transformation isattempted for purposes of starting ignition, the output is grosslyexcessive at running speeds. Either a complex and inefficient switch orregulator must be provided, or a con siderable power waste (by diversionfrom the output of the entire unit) must be tolerated.

The present invention provides a novel solution to this problem, andpermits self-ignition which is adequate for starting and not wasteful ofpower at running speeds.

The invention will best be understood from the following detailedspecification of a preferred embodiment, taken in connection with theappended drawings. However, the embodiment shown and described is merelyexemplary, and may be modified in various respects without departingfrom the scope of the invention as defined in the appended claims. Inthe drawings,

Fig. 1 is a diagrammatic view showing a preferred form of the invention,and

Fig. 2 is a graph showing certain speed-voltage relationships referredto herein.

Referring now to Fig. 1 of the drawings, reference numeral 10 designatesgenerally an internal-combustion engine which may be of any known orconventional design, utilizing a high-tension spark plug 12 for ignitingthe combustible charge in its cylinder. Theshaft of engine 10 isconnected, either directly or through gearing or the like, with therotor of an alternator 14, herein of the permanent magnet type rotatingwithin a field winding structure to induce therein a voltage in wellknown manner. The current output of alternator 114 is available for useat terminals 16, and is also connected by conductors rotation of theengine shaft as by a cam 22 on or con-.

nected to said shaft. For a single cylinder, two-stroke cycle engine, asshown, having a single spark plug, the' points 20 may be arranged toremain open for say 330 of engine rotation, and to close for theremaining 30.

The invention does not depend upon rapid opening of the contacts, asdoes the ordinary induction coil system.

Since the present invention is principally intended for use nearcommunication gear, shielding of the electrical parts is desirable. Forthis and other reasons, it is preferred to house the parts now to bedescribed in a metallic shielding container designated by numeral 24.For clarity, the container is shown enlarged, and the drawing isintentionally out of scale in this respect.

The conductors 18 enter container 22 through conventional feed-throughcapacitors 25, 26 provided to reduce transmission of radio-frequencynoise over those conductors. The conductors then pass to the; primarywinding 23 of an iron-core regulating transformer 30 having the shuntleg 32 containing an air-gap 34 dimensioned to saturate in a knownmanner to provide a desired nonlinear transformer characteristic as willbe described. The capacitor 36 is shunted across the primary winding 28to compensate for the lagging power factor of transformer 30.

The regulated output voltage of transformer 30 appears across itssecondary winding 38, one terminal of which is connected to shield orcontainer 24 and to the engine block (or otherwise) to one side of sparkplug 12. Capacitor 40 is shunted across secondary 38 and (it beingremembered that the alternator frequency will be lower at low speed thanat normal running speed) has a value such as will approximately resonatethe secondary winding 38 at the low frequency generated at the startingphase. A rectifier, such as a dry disc rectifier 42 is in series withthe circuit to ignition (high tension) transformer primary winding 44,the circuit being completed periodically through contact points 20 asdescribed above. A capacitor 46 is connected to be charged, throughrecti- Patented Nov. 27, 1 956 fier 42, during the relatively longintervals when contacts 20 are open, and the rectifier prevents it fromdischarging through winding 38 during periods of reduced or reversedvalue of the alternator voltage.

When contacts 20 are closed by cam 22, capacitor 4-6 discharges throughprimary winding 44 of the conventional ignition or spark transformer 48.The core may be connected to the start end of the secondary or highvoltage winding 50 wound on the core, with the primary wound over thesecondary and suitably insulated. The value of storage capacitor 46 ischosen to provide maximum energy transfer to primary Winding 44, andthis produces the required voltage in secondary 50 for operation of thespark plug 12.

Fig. 2 illustrates by curve A the linear relation between engine speedand alternator output, and shows that for adequate voltage output (forignition purposes) at running speed the value at starting (cranking)speeds would be Wholly inadequate. The non-linear characteristic ofsaturable transformer 30, in combination with capacitors 36 and 40,effectively raises the voltage output at starting to a value which maybe greater than normal for full running speed, and which is maintainedat nearly that level even at full speed. In any event, it is plain thatadequate voltage for ignition is available at the relatively lowalternator speed obtained during the cranking operation. A somewhathigher-than-average ignition voltage is preferred for starting, as theengine, and the combustible charge, are apt to be cool, and the droopingcharacteristic provides this feature, as well as reduces theignition-energy drain from the useful power output under running speedconditions.

In the form shown, the cam 22 is shown on the engine shaft, but it maybe at the other end of the common shaft, or elsewhere. Also, spark plug12 may be in a separate shield structure from that enclosing theignition regulator components, as may be the cam and contacts 20. Insuch respects, the design may be varied widely to conform'to specialrequirements. These and other modifications may be made withoutdeparting from the invention claimed. By other suitable changes, theinvention may obviously be applied to multi-cylinder engines, or toengines of other than two-stroke cycles.

It will be seen from the foregoing that the system provided is quitesimple, in that a conventional. simple set of contacts 20 are employed,rather than a combined make-break set, for charging and discharging thestorage capacitor. Also, the system provides for automatic reduction inthe ignition power drain when running speed is attained, without anymanual or centrifugal switch being required. Contact protection (such asthe usual shunt capacitor) is not required, as contacts 20 open onlyafter the storage capacitor is substantially discharged and only a lowvoltage, if any, then appears across the contacts. The rectifier 42 issimple and reliable, since it receives only the relatively low voltageapplied to capacitor 46 across the primary of the spark transformer. Thesystem operates well with alternators having sine-wave output, so thatno compromise is required in the alternator design with respect to itsuseful output waveform.

What is claimed is:

In combination, an alternator having output terminals and aninternal-combustion engine mechanically coupled to said alternator andincluding an ignition system, said ignition system including aregulating transformer having a pair of input terminals coupled to saidalternator output terminals and a pair of output terminals, a rectifierand a storage capacitor serially connected across said regulatingtransformer output terminals, an ignition transformer having primary andsecondary Windings, and a contact maker, said primary of said ignitiontransformer and said contact maker being electrically connected inseries across said storage capacitor.

2. The combination according to claim 1 in which said alternator andengine are inter-coupled by a shaft which also actuates said contactmaker in predetermined time capacitor intercouples said output terminalsof said regulating transformer.

4. The combination according to claim 3 in which said capacitorresonates the output winding of said regulating transformer at afrequency corresponding to the starting speed of said alternator.

5. The combination according to claim 1 in which said regulatingtransformer includes a saturable core.

6. An ignition system for use with an internal-combustion alternatorcombination, including a regulating transformer having a pair of inputterminals adapted for connection to the output terminals of analternator and a pair of output terminals, a rectifier and a storagecapacitor serially connected across said regulating transformer outputterminals, an ignition transformer having primary and secondarywindings, and a contact maker adapted for mechanical coupling to anengine driving an alternator, the primary of said ignition transformerand said contact maker being electrically connected in series acrosssaid storage capacitor.

References Cited in the file of this patent

